1. Field of the Invention
The invention relates to a paper processing roll, in particular, for use within a paper calender, wherein the roll during operation can be exposed to increased temperature, as well as to a method for producing a roll usable in paper processing, in particular, for use in the calender of a paper-making machine.
2. Description of the Related Art
In paper processing, for example, for glossing or other treatments of the paper surface, a paper web is guided through a roll gap (nip) of a calender arrangement. This is the case in calenders or a glazing apparatus installed online or off-line, independent of their configuration. The continuously increasing production velocities and the multi-nip calenders which are currently on the market pose new requirements in regard to the quality of thermal rolls. Moreover, high-quality paper products which, in the past, have been processed without exception with off-line super calenders at considerably reduced production speeds are glazed increasingly online. This means that the calender arrangement must meet the challenge of the requirements of the paper-making machines with respect to production speed, reliability etc.
Multi-nip calenders of the newest generation make it possible to integrate a calender arrangement directly into the paper-making machines (online operation). This has the result that the calender, respectively, its rolls, must fulfill the requirements of a paper-making machine with, partially, production speeds which are considerably higher than 2,000 meters per minute. Accordingly, the calender rolls, depending on the diameter, rotate at rotational frequencies of up to values just below 1,000 rpm.
In view of the considerable size of conventional calender rolls—length of more than 10 meters, weight of several tens of tons—such an operation can result in considerable loading of the bearings which support the rolls, of the elastic roll covers provided on the counter rolls, as well as of the stands. Disruptive effects, no matter what their origin, can excite vibrations as a result of which the elastic covers will become marked and a uniform running of the rolls can no longer be ensured. The running behavior of the thermal roll can contribute to the occurrence of the widely known, but up to the present not yet solved, barring problem because, possibly, a system-own vibration can be triggered. Erratic running of the roll or the existence of a barring problem often leads to a prematurely required exchange of the rolls and an increased wear of the elastic roll covers, which cause a high economic loss for the operator of such a device.
In off-line calenders this is counteracted in that the production speed is lowered, which however does not solve the problems but simply weakens the effects (marking of the roll covers and of the product). In the case of calenders that are installed online this is not an option. In the course of the development of the new calender concepts and the continuously increasing production speeds and heating efficiencies, dimensional precision of the calender roll with respect to roll shape and concentric running under the operating conditions is of special importance. The roll shape is to be viewed as particularly critical because the calender rolls impart to the paper its optical and haptic properties and deformations of the calender rolls, even in the micrometer range, result in clearly visible imperfections of the paper quality and the properties of the elastic roll covers. The quality requirements for high-quality paper can possibly no longer be fulfilled when the roll shape is not sufficiently precise. In the case of multi-nip calenders, the roll shape is of special significance in the area where the calender roll is clamped between neighboring rolls.
In the case of online soft calenders with a single roll contact, the concentric running quality of the rolls resulting under operational load, relative to the rotational axis, must be considered primarily. Deviations from the roll barrel shape with respect to the spacing to the rotational axis must be avoided in order to prevent effects on the roll gap (nip).